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Air sealing and insulation are the two secrets that allow a thermos to keep hot things hot and cold things cold. The insulated walls of a thermos create a barrier between the contents inside and the air temperature outside, interrupting the natural equilibrium of heat. The top of the thermos has a rubber gasket and screws on to create a tight seal. This prevents air flow, and thus rapid heat exchange via air currents, to maintain the thermal barrier.

Your house works pretty much like a thermos. Insulation prevents heat loss (in the winter) and heat gain (in the summer) through the walls and ceilings, while air sealing prevents heat loss or gain through air movement. Most people think of insulation only to keep out the cold, but according to Nancy Kellogg, a certified energy auditor with Lightly Treading, Inc., improving insulation and air sealing is just as important for the cooling season.

Kellogg once got a call from a client who had recently tightened up her home with insulation and air sealing improvements. It was June and quite warm outside, but the client was uncomfortably cold in the house and was reluctant to turn the heat on in the summertime. “I told her to open the windows,” says Kellogg. Clearly, the house had done its job of isolating the indoors from the outdoors (with somewhat humorous results, in this case).

When it comes to both air sealing and insulation, Kellogg stresses to her clients to “start at the top, and seal up the lid (meaning the ceiling under the attic) really well. This is the most important place to create a barrier. Holes in there are always the strongest for airflow.” This, Kellogg explains, is due to the “stack effect,” the fact the tall structures such as houses act like chimneys to promote warm air rising from natural convection. “And the taller the house, the stronger the stack effect.”

Kellogg also points to garages as other common problem areas. “If you have an attached garage, make sure it’s thermally separated from the house.” She explained that this is a commonly neglected area by builders, leading to significant heat exchange between the house and garage.

For more information about air sealing and insulating your house, Energy Star has a handy DIY manual available on its Web site.